A three-dimensional numerical simulation study has been carried for the Top-Seeded Solution Growth (TSSG) process of single crystal SiC. During growth, Marangoni and forced convections (flows) develop in the growth solution due to free surface tension gradient and seed rotation, respectively. Relative contributions of such flows were numerically examined. Since supersaturation in the growth solution near the crystal surface is a key factor affecting the stability of crystal morphology, our study has focused on the influence of these flows on the distributions of spatial and temporal flow velocity and solution supersaturation. Simulation results show that the contribution of Marangoni convection gives rise to the development of spoke-like flow patterns and a downward flow below the seed crystal that leads to a non-uniform supersaturation distribution at the center and at the edge near the seed crystal surface. Additionally, a characteristic frequency associated with the supersaturation oscillation appears to be due to the Marangoni instability. Results also show that, although the forced convection induced by seed rotation may weaken such supersaturation non-uniformity in the center and suppress the development of such spoke-like patterns, its effect near the edge is not significant.